The invention relates to a rain sensor for a windshield of a vehicle, and more specifically, the invention provides a rain sensor and a small air pump for directing a flow of air with respect to a surface sensed by the sensor.
When an automobile driver travels long distances through rain, the driver must continually adjust the speed of the windshield wipers because the intensity of the rain striking the windshield continually varies. Variation is caused by the natural variation in rain over time and distance, and also by man-made agents, such as passing vehicles which shower the windshield with spray.
This continual adjustment can be tedious. Rain sensors have been developed in order to automate the control of windshield wipers. These sensors generally take the form of conductive sensors capacitive sensors, or optical sensors. In all types of sensors, however, the sensing of moisture is passive in that a moisture collecting surface is simply exposed to the environment. Typically, the moisture collecting surface is the windshield of the vehicle. It would be desirable to manipulate the moisture collecting surface to promote the formation of moisture in proximity to the surface sensed by the sensor before moisture actually collects on the remaining portions of the surface.
The present invention provides an apparatus for actively detecting the presence of moisture on a moisture collecting surface. The apparatus includes a moisture sensor that can detect the presence of moisture on a moisture collecting surface. The moisture sensor can be a conductive moisture sensor, an optic moisture sensor, or a capacitive moisture sensor. The moisture collecting surface can be defined by at least a portion of the windshield of a vehicle. The apparatus also includes means for accelerating the formation of moisture on the moisture collecting surface adjacent to or in proximity to the portion of the surface sensed by the sensor. The means for accelerating moisture formation can be an air pump capable of directing a flow of air with respect to the moisture collecting surface. The air pump can include means for cooling the air to be directed over the moisture collecting surface. The air pump can be formed of a flexible housing having an inlet port and an outlet port and valves to control the flow of air in and out of the ports. An air pump with a flexible housing can be expanded and contracted, similar to a bellows, to draw air into the housing and discharge air out of the housing by a pulsatable member, such as a piezoelectric member. In such an embodiment, the apparatus can include means for alternating the voltage across the piezoelectric member. Accelerating the formation of moisture on the collecting surface can also be accomplished by any means capable of reducing the temperature of the collecting surface to promote condensation. The apparatus can also include a controller for controlling the operation of the air pump or cooling means.
Other objects, advantages and applications of the present invention will become apparent to those skilled in the art when the following description of the best mode contemplated for practicing the invention is read in conjunction with the accompanying drawings.